1. Field of the Invention
The present invention relates to a cooling device adapted to circulate a coolant for cooling a heat generating electronic component such as a central processing unit (hereinafter referred to as CPU) disposed in a housing, as well as to an electronic apparatus including the same.
2. Description of the Related Art
The recent years have seen a dramatic progress in the speed-up of computers while CPUs have much greater clock frequencies than before. As a result, heat generation of the CPU is increased so much that the conventional air cooling method solely dependent upon a heat-sink has become inadequate. In this context, a high-efficiency, high-power cooling device is absolutely required. Known as such a cooling device are those disclosed in Japanese Unexamined Patent Publication Nos. 264139/1993 and 32263/1996 wherein a coolant is circulated on a substrate for cooling the substrate with a heat generating electronic component mounted thereon.
The conventional cooling device for cooling the electronic apparatus by means of coolant circulation will be described as below. It is noted that the term “electronic apparatus” essentially means herein an apparatus adapted to perform processings based on a program loaded in the CPU or the like, or more particularly a portable compact apparatus such as a notebook computer. However, the term also includes other apparatuses equipped with a heat generating electronic component which generates heat when energized. A first conventional cooling device is schematically shown in FIG. 10. Referring to FIG. 10, a reference numeral 100 represents a housing; a numeral 101 representing a heat generating electronic component; a numeral 102 representing a substrate with the heat generating component 101 mounted thereon; a numeral 103 representing a cooler performing heat exchange between the heat generating component 101 and the coolant for cooling the heat generating component 101. A reference numeral 104 represents a radiator for removing heat from the coolant; a numeral 105 representing a pump for circulating the coolant; a numeral 106 representing a pipe interconnecting these elements; a numeral 107 representing a fan for air cooling the radiator 104.
Now, description is made on the operations of the first conventional cooling device. Discharged from the pump 105, the coolant flows through the pipe 106 to reach the cooler 103, where the coolant is raised in temperature by absorbing the heat of the heat generating electronic component 101. Then, the coolant is delivered to the radiator 104, where the coolant is lowered in temperature as air cooled by the fan 107. Thus, the cooled coolant is returned to the pump 105. The movement of the coolant is repeated in cycles. The cooling device is designed to cool the heat generating electronic component 101 by circulating the coolant in this manner.
Next, a second conventional cooling device for electronic apparatus is exemplified by that disclosed in Japanese Unexamined Patent Publication No. 142886/1995. FIG. 11 is a general view of the apparatus with the cooling device.
The second cooling device is designed to cool a heat generating member mounted in a narrow housing by efficiently transferring heat from the heat generating member to a wall of a metal housing which serves as a radiator portion. Referring to FIG. 11, a reference numeral 108 represents a wiring board of an electronic apparatus; a numeral 109 representing a key board; a numeral 110 representing a semiconductor heat generating device; a numeral 111 representing a disc unit; a numeral 112 representing a display unit; a numeral 113 representing a heat absorber header involved in heat exchange with the semiconductor heat generating device 110; a numeral 114 representing a radiator header for heat dissipation; a numeral 115 representing a flexible tube; a numeral 116 representing a metal housing of the electronic apparatus.
The second cooling device is adapted for thermal connection between the semiconductor heat generating device 110 as the heat generating member and the metal housing 116 by means of a thermal transfer device of a flexible structure. The thermal transfer device includes the flat heat absorber header 113 attached to the semiconductor heat generating device 110 and having a fluid passage; the radiator header 114 having a fluid passage and disposed in contact with a wall of the metal housing 116; and the flexible tube 115 interconnecting the headers. The thermal transfer device is designed to drive or circulate a fluid sealed within the device between the heat absorber header 113 and the radiator header 114 by means of a fluid driving mechanism incorporated in the radiator header 114. Thus, an easy connection between the semiconductor heat generating device 110 and the metal housing 116 is provided irrespective of component layout. Furthermore, a highly efficient heat transfer is accomplished by driving the fluid. Since the radiator header 114 is thermally connected with the metal housing 116, the heat from the radiator header is diffused widely on the body of the metal housing 116 having a high heat conductivity.
On the other hand, there is known a pump with a heat exchange function for internal heat exchange, as disclosed in Japanese Unexamined Utility Model Publication No. 147900/1990. The pump with the heat exchange function is shown in a partially cut-away perspective view of FIG. 12. Referring to FIG. 12, a reference numeral 120 represents a motor; a numeral 121 representing a heat exchanger; a numeral 122 representing a cooling water passage; a numeral 122a representing an outlet port; a numeral 122b representing an inlet port; a numeral 123 representing a centrifugal pump; a numeral 124 representing a housing; a numeral 125 representing an impeller.
The centifugal pump 123 is provided with an inlet port 124b centrally of the housing 124 of a volute type, and with an outlet port 124a tangentially of the housing. Disposed within the housing 124 is the impeller 125, a shaft of which is coupled with the motor 120. The cooling water passage 122 of the heat exchanger 121 is accommodated in the housing, as arranged on the whole outer periphery of the impeller 125 in a zigzag fashion.
Now, description is made on the operations of the conventional pump with the heat exchange function. When the impeller 125 is rotated by the motor 120, a heated coolant A from the apparatus is introduced into the housing 124 via the inlet port 122b to be whirled in the housing 124 and then discharged from the outlet port 122a on the external side. In this process, turbulent flow is formed at an outer area of the interior of the housing 124 because of high pressure, thus violently bringing the coolant A into contact with the cooling water passage 122 so that the coolant A is cooled by a cooling water B flowing through the cooling water passage 122. In this manner, the device delivers the coolant A to the apparatus under pressure while cooling the coolant A in the centrifugal pump 123.
However, the first conventional cooling device described above requires the cooler 103 for cooling the heat generating electronic component 101 by way of heat exchange between the heat generating component 101 and the coolant, the radiator 104 for removing the heat from the coolant, and the pump 105 for circulating the coolant. Since the cooling device comprises the combination of these elements, the device has a large and complicated structure which cannot be downsized and also involves cost increase. In other words, the first conventional cooling device is basically suited for cooling large electronic apparatuses but is not adapted for the current high-performance portable notebook computers featuring a compact, lightweight and slim design and various modes of carriage and use.
Although the aforementioned second conventional cooling device can be adapted for use in the notebook computers, the flat heat absorber header 113 attached to the semiconductor heat generating device 110 and the radiator header 114 in contact with the wall of the metal housing 116 are both shaped like a box, having substantial thickness. That is, the headers are an impediment to a thinner design of the notebook computer. Specifically, the second conventional cooling device is arranged such that the radiator header 114 contains therein a reciprocating pump as the fluid driving machine which is smaller in transverse width than other pumps. Unfortunately, the thickness of the reciprocating pump defines a great thickness of the radiator header 114 as a whole, making the notebook computer of slim design impracticable.
Further, the slim notebook computer does not permit the heat absorber header 113 to accommodate the reciprocating pump of the second cooling device. That is, the thickness of the pump would add to that of the semiconductor heat generating device 110, resulting in an increased thickness of the notebook computer. This is against the movement toward the thin design of the notebook computers. In addition, vibrations and noises produced by the reciprocating pump adversely affect the semiconductor heat generating device 110 on which the pump would be mounted. In some cases, the noises may grate on ear. On these accounts, it is difficult for the second cooling device to contribute the slim design.
The second conventional cooling device encounters a limited cooling capability because the radiator header 114 in contact with the wall of the metal housing 116 has a low heat transferability resulting from a small heat radiating area. It may be contemplated to increase the heat radiating area for enhancing the cooling capability. However, the further increase of the heat radiating area leads to the following contradiction. That is, the increased heat radiating area means an increased length of the flow passage and amount of circulation, thus requiring an increased output of the incorporated reciprocating pump, which results in an increased thickness of the radiator header 114. If an arrangement is made such that the reciprocating pump is independently accommodated in the metal housing 116, another space for the pump must be spared in the body of the notebook computer with dead space reduced to the limit. Furthermore, assembly work for the cooling device is complicated. Thus, the second conventional cooling device has limitations in the reduction of size and thickness of the notebook computers. The second conventional cooling device with such drawbacks falls short of meeting a demand for further increase of the cooling capability in conjunction with the recent progress of the CPUs.
On the other hand, the conventional pump with the heat exchange function has a large, complicated structure requiring the cooling water passage disposed therein because the coolant is cooled by the independent cooling water. The pump further requires a second pump for circulating the cooling water and a second heat exchanger for absorbing heat from the cooling water. Hence, the pump is a complicated system difficult to be downsized and also suffers a large number of components and low assembly efficiencies. Consequently, a good thermal efficiency or cost reduction cannot be expected from this pump.
In view of the foregoing, it is an object of the invention to provide a cooling device accomplishing both the improved cooling efficiency and the reduced size and thickness thereof, and featuring a simple construction.
It is another object of the invention to provide an electronic apparatus featuring a compact, slim design and a simplified construction.